This invention relates to vibration welding generally and more specifically to a method and apparatus for setting up a vibration welder to vibration weld a work-piece.
In the operation of a vibration welder a work-piece is loaded onto the machine between fixtures on the platen, one of which is then pressed towards the work-piece. One of the platen and its associated fixture are vibrated at a mechanical resonance frequency to achieve a weld of a material to the work-piece. There are many patents describing vibration welders as well as so-called orbital welders, all of which are referred herein as vibration welders.
Since the fixture and the associated mass of the vibrating platen and mechanical springs and components are significant the amount of power needed to achieve the proper relative motion to achieve a vibration weld is also substantial. In order to obtain sufficient motion between the material and the work-piece, it is desired to operate the vibration welder at the mechanical resonance of the active platen and its fixture. Since the resonance frequency varies with different fixtures and platen loadings a common technique to determine the resonance of the vibration welder involves increasing the frequency of the vibration welder to manually determine the resonance frequency where maximum vibration amplitude occurs. This involves a somewhat slow process with a number of iterations to arrive at a proper determination of the resonance frequency since the Q value of the mechanical structure is very high and the resulting resonance curve very narrow. It is not unusual the bandwidth of the resonance curve is of the order of a fraction of a cycle or Hz.
The known manual determination of the resonance frequency is a relatively slow process and affects the efficiency of the use of the vibration welder when changes of work-pieces and fixtures requires a re-tuning of the vibration welder to a new resonance frequency associated with a new fixture and work-piece.
It is, therefore, an object of the invention to provide a method and apparatus to rapidly tune a vibration welder to its resonance frequency. It is a further object of the invention to enable a rapid automatic determination of a desired operating frequency of a vibration welder and its associated fixture. It is still further an object of the invention to rapidly determine the resonance frequency of a vibration welder and its fixture so as to reduce the set-up time for the welder.
One technique to tune a vibration welder in accordance with the invention involves selecting a vibration amplitude reference level and then begin sweeping the operating frequency of the vibration welder in one direction and storing the value of the frequency when the reference amplitude level is sensed. The operating frequency of the vibration welder is then swept in the opposite direction and the frequency is stored when again the sensed vibration amplitude matches the reference level. The desired operating frequency of the vibration welder is determined from the stored frequencies.
When the desired vibration welder operating frequency is the resonance frequency a simple arithmetic operation can be used to determine that. Thus the first and second stored frequency values are added and the sum divided by two to arrive at the resonance frequency for the vibration welder.
As a result of the invention it is not necessary to manually hunt for or determine the resonance frequency directly and the technique of the invention speeds up the determination of the proper resonance frequency. Vibration welder set ups for different work-pieces and fixtures can now be achieved more efficiently and accurately.